The Nature of Science 39.4 Changing levels of carbon dioxide
Seasonal levels of carbon dioxide in the atmosphere Levels of carbon dioxide in the atmosphere change at different times of the year. During spring and summer the days are longer so more photosynthesis occurs. This means that more CO2
removed from the atmosphere and levels are lower. In autumn and winter the days are shorter and leaves fall off trees, so less photosynthesis occurs. This means that less CO2
the atmosphere and levels are higher. is is removed from
Fig. 7 Monthly average CO2
at Mauna Loa, Hawaii.
The red dots on the graph in Fig. 7 represent the monthly average values of atmospheric carbon dioxide in Mauna Loa Observatory, Hawaii. This graph shows that carbon dioxide levels are rising every year.
Carbon sinks
Fig. 8 Forests are natural carbon sinks.
Carbon sinks are reservoirs that store large amounts of carbon compounds. The main natural carbon sinks are oceans and forests. The oceans are the largest carbon sinks. They absorb around one third of the carbon dioxide in the atmosphere. Trees and other plants absorb carbon dioxide from the atmosphere during photosynthesis and store carbon in wood and other structures. When trees are cut down, they cannot remove carbon dioxide from the atmosphere and the carbon they have stored is released when they decompose or are burned.
39.5 The global carbon budget 422
The global carbon budget is a way of describing the amount of carbon dioxide being released into the atmosphere compared with the amount being removed from it. In a balanced carbon budget the rate at which carbon dioxide is released into the atmosphere is approximately the same as the rate at which it is removed.
